The present invention is broadly applicable to a process for electrolytically stripping or removing unwanted metallic deposits or platings from substrates, and more particularly, for electrolytically stripping unwanted nickel and nickel alloy plating deposits from cooper and copper alloy basis metals or substrates.
The stripping or removal of nickel and nickel-alloy deposits such as nickel-iron alloy deposits, is ocassionally required when the metal plating is defective or has become mechanically damaged during the handling of the article. By stripping or removing the defective or damaged electrodeposit, the article can be salvaged and subsequently replated to provide a commercially satisfactory article. The stripping of nickel and nickel-alloy metal deposits is of significant commercial importance in the plumbing fixture industry in which the fixtures are comprised of copper or copper alloys, usually brass, over which a bright nickel or nickel-iron alloy plating is deposited to enhance appearance and durability. A problem heretofore associated with the stripping of such nickel and nickel-alloy deposits from copper and copper alloy substrates has been the tendency of the stripping composition or the process for effecting such stripping to cause adverse etching or damage to the substrate necessitating expensive refinishing operations to restore the substrate to a condition in which it can be replated.
In accordance with prior art practices, it has been conventional for stripping nickel and nickel-alloy electrodeposits from copper and copper alloy substrates by employing relatively concentrated acidic solutions such as hydrochloric acid and sulfuric acid alone or in further combination with phosphoric acid to effect a removal of the electrodeposit. Such concentrated acidic solutions have a tendency to etch and pit the basis metal and also present handling and waste disposal problems because of the corrosive nature and high concentration of such stripping solutions.
The process and stripping solution of the present invention overcomes many of the disadvantages and problems associated with prior art techniques by providing a stripping solution which is relatively dilute and therefore less corrosive facilitating its handling and disposal while at the same time providing for an efficient rate of stripping and a lower attack rate on the copper or copper alloy basis metal eliminating etching or pitting of the basis metal. Accordingly, only a light color buffing of the stripped article is usually required to restore its high lustre to enable the replating thereof. Particular benefits are achieved in the stripping of bright nickel and nickel-iron electrodeposits containing up to about 40 percent iron from brass plumbing fixtures enabling a replating thereof to provide a commercially satisfactory product.